In man, the primary objective of genetic studies is to determine the genetic and cultural modes of transmission, through a resolution of (1) the additive, dominance and epistatic genetic components of variance and (2) specific environmental effects such as maternal factors and common sibling environments. Due to previous methodological limitations, such information are presently nonexistent for dental developmental traits. Only recently has an innovative genetic model been described that is suitable to test the genetic and cultural basis of complex multifactorial traits, through the offspring of identical twins who are genetically half-sibs. This project is a pilot study with the aim of testing this new model for its effectiveness in resolving the components of dental trait variation. From a unique panel of male and female identical twins together with their spouses and offspring, dental size and other variables will be examined. The analysis of variance, both univariate and multivariate, will be used to partition the subcomponents of genetic and environmental variances as well as to delineate important maternal effects. Controlled animal studies have consistently demonstrated striking evidences for maternal influence on the dentition. For humans, this project represents the first study designed to search for maternal determinants of dental traits in normal singleton births.